A technique called thin provisioning has been developed with the aim to facilitate management of storage subsystems and to enhance the efficiency of capacity thereof. This technique is for providing a virtual logical volume that does not have a physical storage area (hereinafter abbreviated as virtual volume) from the storage subsystem to a host computer, and dynamically allocating pages from a real pool which is a physical storage area in response to writing of data from the host computer to the virtual volume. A page refers to a single unit when the storage area is divided into multiple areas. This technique enables to enhance the capacity efficiency of a storage subsystem and to facilitate capacity design.
Another technique for realizing enhanced capacity efficiency is a compression technique that reduces the amount of data by compressing the data stored in the storage subsystem. For example, patent literature 1 teaches a method for compressing the data within a virtual volume using thin provisioning technique.